Melinda Gates, who is Co-Chair of the foundation as well as Co-Chair of the WEF annual meeting, added that the couple have been "investing in vaccines for over 10 years."

That investment has resulted in saving the lives of three million kids. With that statistic in mind, Melinda expects "another eight million lives can be saved by the new vaccines that are coming out and by delivering the existing vaccines."

Their investment is "a signal of our enthusiasm of what we think can be done."

Bill Gates broke it down for us and explained where the $10B donation will go.

Their priorities:

1. Getting coverage of vaccines to more children

2. Adding vaccines that have already been invented in the rich world and getting that out to the poor countries

3. Inventing new vaccines

And in perhaps a return to his roots, Bill Gates is increasing his online presence.

On January 19th, he made his first tweet and since then, he's added 398,588 followers and counting! Aside from Twitter, he's also re-emerged on Facebook and launched a new Web site called The Gates Notes.